Patent GB-914185-A (GB)
Title: Improvements in or relating to chart position display apparatus
Inventor: ROBERTS GRAHAM ESTYN
IPC: G01S5/10
Filed: 1960-11-09
Abstract: 914,185. Course recorders. DECCA Ltd. Nov. 6, 1961 [Nov. 9, 1960], No. 24536/61. Divided out of 914,183. Class 97 (2). [Also in Group XL (c)] Relates to means for recording the track of a craft in accordance with the x and y coordinates Lx, Ly of the craft as computed from position data provided by a radio navigation system in which a chart strip 36 mounted on rollers 38 is moved longitudinally in accordance with the co-ordinate value Ly by means of a servomotor 53 driving the rollers 38 and a recording stylus 39 is moved transversely across the chart in accordance with the co-ordinate value Lx by means of a leadscrew 42 driven by a servomotor 43. According to the present invention, the longitudinal position Y of the chart 36 is determined in the form of an electrical digital signal by fixed sensing means 49 in conjunction with position code marks 48 along the edge of the chart, the transverse position X of the stylus 39 is determined in similar form by sensing means 47 attached to the stylus carrier 41 and operating in conjunction with fixed position code marks 46, digital signals corresponding to the craft co-ordinates Lx, Ly are derived in a digital computer 35 and the digital signals Lx, X and Ly, Y are combined in the computer 35 to give digital error signals Er = Lx - X and Ey = Ly - Y which are converted to corresponding analogue signals and applied to actuate the X and Y servomotors 43 and 53, respectively, to maintain X=Lx and Y=Ly. As shown, additional fast X and Y drive-motors 44, 54 are provided; each pair of slow and fast motors 43, 44 and 53, 54 is coupled to its respective driven member through a differential 45, 55 and means are provided for energizing the fast motors 44, 54 (1) by manual controls 56, 57 when it is required to adjust the initial position of the chart and (2) by the error signals Ex and Ey when the errors Er and Ey exceed first predetermined values, the circuit being switched back to the slow speed motors 43, 53 when the errors Er and Ey are less than the second predetermined values which are less than said first predetermined values. Means are also provided for ensuring that the stylus 39 does not mark the chart when the fast motors 44, 54 are in operation or until the errors Er, Ey have been reduced to zero. As described, each of the sensing means 47, 49 comprises a plurality of photo-cells producing a nine-digit position signal in Gray code; alternatively, the X position sensing means may comprise brushes moving over fixed contacts. The stylus 39 may be arranged underneath the chart 36 and may be pressed against the chart by a solenoid; it may be an ink stylus or it may press a marking ribbon against the chart. The invention is described as used in conjunction with a hyperbolic radio navigation system of the type disclosed in Specification 620,479 comprising a master transmitter and three spaced slave transmitters in which the three hyperbolic co-ordinates of the craft are given by the angular positions of the output shafts of three phase meters 20, 22, 24. As shown, each of these angular positions is expressed as a 15-digit Gray code by a corresponding digit disc 21, 23, 25 and the three signals are applied to the computer 35 via respective gates 30, 31, 32, a common OR gate 33 and a Gray-to-binary converter 34, the corresponding cartesian coordinates Lx, Ly being then computed in the computer 35 as functions of the most appropriate pair of hyperbolic co-ordinate valves A and B and a number of constants whose values depend on the known positions of the master and slave transmitters. In order to cover an extensive track, a plurality of chart sections which may be drawn to different scales are arranged in a strip with a space between adjacent sections and the computation constants relating to any one chart section are given by code marks 59 in the space preceding said chart section, corresponding signals being read out to the computer 35 by the Y sensing means 49 when the section is moved into position by actuation of the fast Y drive motor 54; the marks 59 also include components which produce signals controlling the gates 30, 31, 32 to select the most appropriate pair of hyperbolic co-ordinate signals.